The present invention relates to a galvanic cell using a solid electrolyte.
A liquid electrolyte has been used as the electrolyte for conventional galvanic cells. However, it caused leakage of the liquid and had problems in long-term reliability and stability.
The solid electrolyte has been investigated considering this point of view. .beta.-alumina, lithium iodide, lithium nitride and copper rubidium, etc. have been known as the solid electrolytes. However, they have problems in moldability and film-formability.
Hence, various investigations have been carried out on the organic-solid electrolyte which can solve the problems in moldability and film-formability. For example, there has been known the following organic solid electrolytes: an organic polymer electrolyte of polyethylene oxide (PEO) type; an organic polymer electrolyte having a multifunctional polyether molecular structure prepared by a randam copolymerization of ethylene oxide portion and propylene oxide portion (Japanese Laid-Open Patent Publication No. 249,361 of 1987); a solid polymer electrolyte comprising an ethylene oxide copolymer containing an ionic compound in dissolved state (Japanese Laid-Open Patent Publication No. 83,249 of 1986); and an ion-conductive polymer electrolyte in which a high polymer solid substance having plasticity is further constituted substantially with a branched-chain of a homopolymer or copolymer which is thermoplastic and has no crosslinkage (Japanese Laid-Open Patent Publication No. 98,480 of 1980).
However, in a straight chain PEO, crystallization of PEO occurs at a temperature lower than its melting point to lower the ionic conductivity suddenly. In the other polymer electrolytes, though the conductivity at room temperature of about 25.degree. C. is improved by the inhibition of crystallization, no sufficient conductivity usable in a galvanic cell can be attained at a temperature lower than it and especially an extreme decrease in conductivity is observed at 5.degree. C. or lower.
An object of the present invention is to provide a galvanic cell which eliminates the above problems and can be used stably at a low temperature and has an improved low temperature characteristics.